P07B8
Transmission Park Position Sensor/Switch B Circuit/Open.
- Generic
- Powertrain
- Generic code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 7
- AreaTransmission
- B8
- FaultThe specific fault in that area
What it means
P07B8 means the transmission control unit has detected an open circuit or a fault in the electrical signal from Park position sensor or switch 'B'. The sensor tells the control unit whether the transmission is in Park. The unit saw a missing, out-of-range or implausible signal on that circuit, for example when compared with circuit A or the selector position. The exact sensor location and layout depend on the vehicle and transmission.
Symptoms
- Warning light on, possibly with a transmission or gearbox warning message
- Engine will not crank, or cranks only in Neutral, because the start permission is not given
- Gear selector position shows incorrectly or flickers on the dashboard display
- Reverse lights or shift lock release not working correctly
- Harsh, delayed or restricted gear engagement, or the car defaults to a limited mode
- Intermittent faults that come and go with wiggling of the selector or with vibration
Possible causes
- Damaged, corroded or loose wiring or connector on the Park position sensor/switch B circuitlikely
- Faulty Park position sensor or switch, or an internal fault in the selector or range sensor assemblylikely
- Misadjusted or worn selector linkage or cable so the switch does not read Park properlypossible
- Water or fluid ingress into the transmission connector or sensorpossible
- Low or unstable supply voltage or poor earth to the sensor or control unitpossible
- Faulty transmission control unit or internal mechatronic faultrare
How to diagnose
- Read all stored codes and freeze frame data, noting any related codes for the A circuit, range sensor or battery voltage, then check for a software update or technical bulletin for the model
- Check the battery condition and charging voltage, as low voltage can cause false circuit faults
- Inspect the sensor wiring, connector and any harness chafe points for damage, corrosion, moisture or pushed-out pins
- Use live data to watch the Park and selector position signals while moving the selector through each position, and compare circuit A with circuit B
- Check the selector cable or linkage adjustment and look for wear or looseness, following the manufacturer's procedure
- Wiggle the harness and connector with the signal monitored to find intermittent faults
- Test the circuit with a multimeter for continuity, short circuits and correct supply and earth, using the wiring diagram for that vehicle
- Check the sensor's resistance or signal against specification, as the sensor type and location vary by model
How to fix
- Repair or replace damaged wiring, terminals or the connector, and seal out any moisture
- Replace the Park position sensor or switch, or the range sensor assembly, if it fails testing
- Adjust or repair the selector linkage or cable so the sensor reads Park correctly
- Restore a good power supply and earth, and charge or replace a weak battery
- Apply a manufacturer software update if an outdated calibration is a known cause for that model
- Repair or replace the transmission control unit only after the wiring and sensor are proven good
Can I keep driving?
The car may still be driveable, but it could refuse to start or fail to register Park, so fix it soon. Always use the handbrake when parked, and avoid relying on Park alone, especially on slopes.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.